Reduced Drag Centralizer

ABSTRACT

An apparatus according to one or more aspects of the present disclosure comprises at least two centralizers, each centralizer having a circumferential stand-off portion and a second circumferential portion defining 360 degrees, at least two bows extending between opposing collars within the stand-off circumferential portion; wherein the at least two centralizers are spaced axially apart and fixedly attached to the tubular with the respective circumferential stand-off portions angularly offset from one another to provide 360 degrees of standoff. According to one or more aspects of the present disclosure, one or both of the collars of each centralizer may be rotationally stationary relative to the tubular and axially moveable relative to the tubular.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Ser. Nos. 61/167,482 filed on Apr. 7, 2009, 61/221,716 filed on Jun. 30, 2009, 61/237,202 filed on Aug. 26, 2009, 61/263,218 filed on Nov. 20, 2009, and 61/287,665 filed on Dec. 17, 2008, all of which are hereby incorporated by reference herein.

BACKGROUND

This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.

Oilfield tubulars are disposed in wellbores to perform various tasks. In some applications, a centralizer may be disposed with (e.g., on) a tubular string to position the tubular string within the wellbore (e.g., wall of the borehole, inner wall of an outer tubular such as the casing, liner, etc.). The centralizer is commonly utilized to maintain separation between the tubular string and the wellbore. Centralizers commonly comprise a pair of collars that are interconnected with bows. The centralizers are positioned on the tubular string with the tubular extending through the respective bores of the collars and the bows extending outward from the tubular string. Centralizers may be fastened to the tubular in various manners. Commonly, centralizers are attached to a tubular such that centralizer is axially moveable along a length of the tubular, for example between stop collars, or one end (e.g., collar) is fixedly attached at an axial position and the other collar being free to move axially. In many configurations the centralizer is rotationally moveable relative to the tubular. At least one of the ends (e.g., centralizer collars) is axially moveable to allow substantial collapse of a bow to facilitate running the tubular string and centralizer through tight spots (e.g., restrictions) in a wellbore.

FIG. 1 is a schematic of a centralizer disposed in a wellbore. Centralizer 3 comprises opposing cylindrical collars 4, 5 and a plurality of bow members 6 attached between the opposing collars 4, 5. A plurality of bows 6 are provided so as to form a 360 degree circumferential diameter to provide 360 degrees of standoff from the wellbore wall. Opposing collars 4, 5 receive tubular 7 (e.g., tubular string) therein and are axially and rotationally moveable relative to tubular 7. Stop collars 8, 9 attached (e.g., fastened) on opposing sides of collars 4, 5 and spaced apart such that centralizer 3 can move axially between stop collars 8, 9. Stop collars 8, 9 may be attached to tubular 7 in various manners so as to be fixed at least axially relative to tubular 7. For example, and without limitation, stop collars 8, 9 may be secured in via clamping (e.g., set screws, nuts, bolts), adhesives (e.g., epoxy), welding, crimping, and interference fits. Centralizer 3 and tubular 7 are disposed in a (e.g., substantially cylindrical) wellbore 10 defined by wall 12. In FIGS. 1 and 2, wall 12 is depicted as a tubular (e.g., casing, liner, tubing).

FIG. 2 illustrates a centralizer being passed through a restriction in the wellbore. FIG. 2 depicts wellbore 10 having a restriction 14. Restriction 14 is used generally herein to describe a reduced inside diameter portion of wellbore 10. The restriction 14 may be formed intentionally (e.g., a transition) or unintentionally (dogleg, turn, sloughing, etc.). In this embodiment, restriction 14 is a tubular having an inside diameter less than the tubular section depicted at the left side of FIG. 2.

In FIG. 2, centralizer 3 and tubular 7 are being moved to the right, which may be gravitationally vertical, deviated from vertical, or horizontal. To move into and through restriction 14, the outside diameter of centralizer 3 must be less (e.g., collapsible to less) than the inside diameter of the restriction 14. Thus, in the depicted embodiment of FIGS. 1 and 2, opposing collars 4, 5 are allowed to move axially away from each other so that bows 6 can collapse radially toward tubular 7. It is noted that one or both of the collars may have at least limited axially movement. When centralizer 3 is moved through restriction 14, into an increased diameter portion of the wellbore, bows 6 will “spring back”, pulling collars 4, 5 axially toward each other and providing stand-off relative to the wellbore wall.

In order to move through restriction 14, the running force must be sufficient to overcome the collapse load (e.g., stand-off force) of the centralizer and the frictional forces of running the tubular string. Typically, this requires that the running forces (e.g., collapse and friction) must be less than the weight of the tubular string. Thus, in some applications it is necessary to provide centralizers that have a low collapse force to reduce the tubular running and starting forces to pass through the restriction. However a low collapse force (e.g., low restore force, low stand-off force) utilized for bows 6 of centralizer 3 may not have a sufficient restoring or stand-off force to position the tubular string in the wellbore (e.g., centralize) after passing through the restriction. The lack of sufficient stand-off force may be amplified in high-angle and horizontal wellbore sections.

SUMMARY

According to one or more aspects of the present disclosure, an apparatus comprises opposing collars spaced apart from one another along a longitudinal axis, each of the opposing collars adapted to be fixedly secured to a tubular with a holding force; and a bow extending between the opposing collars, the bow having an apex and a stand-off force. The centralizer may comprise one or more bows. The centralizer may include a circumferential portion of at least 180 degrees in which bows are not disposed.

According to one or more aspects, an apparatus of the present disclosure comprises opposing collars spaced apart from one another along a longitudinal axis, each of the opposing collars adapted to be fixedly secured to a tubular with a holding force; and two or more bows extending between the opposing collars, each of the two or more bows spaced apart from one another within a circumferential arc no greater than about 180 degrees.

An apparatus according to one or more aspects of the present disclosure comprises at least two centralizers, each centralizer having a circumferential stand-off portion and a second circumferential portion defining 360 degrees, at least two bows extending between opposing collars within the stand-off circumferential portion; wherein the at least two centralizers are spaced axially apart and fixedly attached to the tubular with the respective circumferential stand-off portions angularly offset from one another.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a schematic view of a centralizer disposed in a wellbore.

FIG. 2 is a schematic view of the centralizer of FIG. 1 disposed in a restriction in the wellbore.

FIG. 3 is a perspective view of a centralizer according to one or more aspects of the present disclosure.

FIG. 3A is an end view of the centralizer of FIG. 3.

FIG. 4 is a schematic view of a centralizer system according to one or more aspects of the present disclosure disposed in a wellbore.

FIG. 4A an end view of the centralizer system of FIG. 4 according to one or more aspects of the present disclosure.

FIG. 5 is a schematic, end view of a centralizer according to one or more aspects of the present disclosure.

FIG. 6 is a schematic, end view of another embodiment of a centralizer according to one or more aspects of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact.

As used herein, the terms “up” and “down”; “upper” and “lower”; “top” and “bottom”; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth of the well being the lowest point, wherein the well (e.g., wellbore, borehole) is vertical, horizontal or slanted relative to the surface. The terms “pipe,” “tubular,” “tubular member,” “casing,” “liner,” “tubing,” “drill pipe,” “drill string” and other like terms can be used interchangeably. The terms may be used in combination with “joint” to mean a single unitary length; a “stand” to mean one or more, and typically two or three, interconnected joints; or a “string” meaning two or more interconnected joints.

According to one or more aspects of the present disclosure a centralizer has collars adapted to be fixedly attached (e.g., at least rotationally stationary) to a tubular and a bow extending between the opposing collars is provided. According to one or more aspects of the present disclosure, a centralizer is adapted to pass through a restriction (e.g., reduced diameter) without requiring collapse of the bow according to one or more aspects of the present disclosure. It is recognized that bow(s) may deflect toward the tubular when running tubular operations; however, this limited deflection is permitted and is not an example of collapse.

FIG. 3 is a schematic view of a centralizer 20 according to one or more aspects of the present disclosure. Centralizer 20 comprises opposing collars 21, 22 and at least one bow 24. Opposing collars 21, 22 comprise bores 25 for receiving and disposing a tubular 7 (See FIG. 1) along the longitudinal axis “X” of centralizer 20. In the depicted embodiment of FIG. 2, centralizer 20 comprises two bow members 24 which each have one or more apexes 28 that extend radially away from the longitudinal axis X of centralizer 20. As described further below, centralizer 20 does not include a plurality of bows 24 spaced around collars 21, 22 to form a 360 degree circumferential diameter at the centralizer 20.

Collars 21, 22 are adapted to fixedly attach (e.g., fasten, secure) centralizer 20 to a tubular. In the depicted embodiment, collars 21, 22 fixedly secure centralizer 20 so as to be axially and rotationally fixed relative to the tubular. In one embodiment, collars 21, 22 are only rotationally fixed relative to the tubular. Opposing collars 21, 22 are depicted in FIG. 3 as an interference fit (e.g., collet) collar having a high holding force, for example 80,000 pounds of axial force. Additional examples of collars include, without limitation to, the attachment collars disclosed in Provisional Application Nos. 61/167,482, 61/221,716, 61/237,202 and 61/287,665 which are incorporated herein. In the depicted embodiment, bow(s) 24 may also have a high stand-off (e.g., restoring force) relative to traditional centralizers as will be understood by those skilled in the art that have benefit of the present disclosure. Bows 24 may be substantially rigid relative to the collapse force of traditional centralizer bows. Centralizer collars 21, 22 may comprise other means and/or mechanisms for fixedly attaching to the tubular.

FIG. 3A is an end view of centralizer 20 of FIG. 3. In this embodiment, centralizer 20 has two bow members which are circumferentially spaced apart from one another. Bow members 24 extend outward (e.g., radially) from the longitudinal axis of the centralizer to their respective apex 28. In this example, the two bow members are spaced about 90 degrees from one another. The number of bows 24 and/or the spacing between bows 24 may be selected such that the positive outside diameter (e.g., the diameter of the uncompressed bows across an apex) of the centralizer is less than a known or expected restriction 14 (FIG. 1) and is not limited to the depicted embodiments. The positive outside diameter of centralizer 20 is depicted by the dashed line and the numeral 30 in FIG. 3A.

FIG. 4 is a schematic view of the centralizers of FIGS. 3 and 3A utilized in a wellbore. According to one or more aspects of the present disclosure, two or more centralizers 20 are attached axially along a section 7 b of tubular string 7 and oriented such that the plurality of bows 24 are spaced 360 degrees circumferentially around section 7 b to provide 360 degrees of standoff from the wellbore wall. For example, centralizers 20 a, 20 b of FIG. 4 each comprise two bows 24 as depicted in FIGS. 3 and 4 which are spaced approximately 90 degrees from one another. Centralizers 20 a, 20 b are fixedly attached along section 7 b and offset angularly so that the four bows are spaced 360 degrees around tubular 7. For example, the centralizer 20 a on the left side of FIG. 4 is oriented with its one bow 24 a positioned approximately 180 degrees from the bow marked 24 a on the centralizer 20 b shown on the right side of the Figure. Similarly, the centralizer 20 a comprises a second bow that is hidden behind tubular 7 and about 180 degrees from bow 24 b on the right centralizer 20 b.

FIG. 4 depicts a restriction 14 in wellbore 10 that is positioned between the left and the right centralizers 20 a, 20 b illustrating that the right centralizer 20 b has passed through restriction 14. The bow members are each depicted contacting wall 12 and substantially centering tubular 7, in particular section 7 b, in wellbore 10 to provide 360 degrees of standoff from the wellbore wall 12. To pass through restriction 14, without collapsing bows 24, the positive outside diameter of the centralizer must be less than the inside diameter of restriction 14. According to one or more aspects of the present disclosure the positive outside diameter 30 (FIG. 3A) of each individual centralizer 20 has a positive outside diameter approximate to or less than the inside diameter of restriction 14, although the total positive outside diameter of the two or more centralizers around tubular section 7 b may be greater than the inside diameter of restriction 14.

FIG. 4A is a schematic end view of the apparatus of FIG. 4. The total or effective positive outside diameter of the two or more centralizers 20 a, 20 b (FIG. 4) is depicted by the dashed line 32. The inside diameter of restriction 14 is depicted by a dashed line circumscribed by the total effective positive outside diameter 32. The individual centralizer positive outside diameter 30 as depicted in FIG. 3A is less than the inside diameter of restriction 14.

Although FIGS. 3 through 4A depict a centralizer having two bows 24 spaced apart approximately 90 degrees, the present disclosure is not limited to the number and/or depicted spacing between the respective bows. For example, each centralizer may comprise a single bow. In single bow centralizer embodiments it may be desired for example to axially space three centralizers with their respective bows angularly offset from one another approximately 120 degrees.

FIG. 5 is a schematic, end view of another centralizer 20 in accordance with one or more aspects of the present disclosure. In this embodiment centralizer 20 comprises two bows 24 a, 24 b which are circumferentially spaced no more than 180 degrees apart. The positive outside diameter of the individual centralizer 20 is denoted by the dashed line 30. A combination of two centralizers 20 of FIG. 5 may be secured to a tubular in a spaced about and angularly offset manner similar to the embodiments depicted in FIGS. 4 and 4A to provide 360 degree circumferential offset. According to one or more aspects, limiting the bows to a circumferential stand-off arc, and or dividing the number of bows required to achieve 360 degrees of stand-off among two or more centralizers facilitates lowering the running force of the tubular string relative to the running force for a tubular string utilizing 360 degrees of stand-off on a single centralize all of which must be compressed to pass through a restriction.

FIG. 6 is a schematic, end view of another centralizer according to one or more aspects of the present disclosure. The depicted embodiment has four bows 24 a, 24 b, 24 c, 24 d circumferentially spaced apart within a circumferential stand-off portion of a centralizer 20 denoted by the numeral 40. In the embodiment depicted in FIG. 6, circumferential stand-off portion 40 is approximately 180 degrees. According to one or more aspects of the present disclosure, circumferential stand-off portion 40 is not greater than about 180 degrees. However, circumferential stand-off portion 40 may be less than 180 degrees as depicted for example in FIGS. 3, 3A.

Corresponding to the limitation of bows 24 being disposed within the circumferential stand-off portion 40 (e.g., arc) is a second circumferential portion 42 (e.g., arc) in which bows 24 are not disposed. Circumferential stand-off portion 40 and second circumferential portion 42 without bows total the 360 degree circumference of centralizer 20.

A combination of two centralizers 20 of FIG. 6 may be secured to a tubular in an axially spaced apart and angularly offset manner similar to the embodiments depicted in FIGS. 4 and 4A to provide 360 degree circumferential stand-off. For example, the circumferential stand-off portions 42 of the respective centralizers are offset from one another.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded. 

1. An apparatus comprising: opposing collars spaced apart from one another along a longitudinal axis, each of the opposing collars adapted to be fixedly secured to a tubular with a holding force; and a bow extending between the opposing collars, the bow having an at least one apex and a stand-off force.
 2. The apparatus of claim 1, comprising a single bow.
 3. The apparatus of claim 1, comprising two or more bows.
 4. The apparatus of claim 1, wherein fixedly secured comprises rotationally stationary and axially moveable relative to the tubular.
 5. An apparatus comprising: opposing collars spaced apart from one another along a longitudinal axis, each of the opposing collars adapted to be fixedly secured to a tubular with a holding force; and two or more bows extending between the opposing collars, each of the two or more bows spaced apart from one another within a circumferential arc no greater than 180 degrees.
 6. The apparatus of claim 5, wherein fixedly secured comprises rotationally stationary and axially moveable relative to the tubular.
 7. An apparatus comprising: at least two centralizers, each centralizer having a first circumferential stand-off portion and a second circumferential portion together defining 360 degrees, at least two bows extending between opposing collars within the stand-off circumferential portion, wherein the at least two centralizers are spaced axially apart and fixedly attached to the tubular with the respective circumferential stand-off portions angularly offset from one another to provide 360 degrees of standoff.
 8. The apparatus of claim 7, wherein the second circumferential portion is at least about 180 degrees.
 9. The apparatus of claim 7, wherein fixedly secured comprises rotationally stationary and axially moveable relative to the tubular.
 10. An apparatus comprising: at least three centralizers, each centralizer having a first circumferential stand-off portion and a second circumferential portion together defining 360 degrees, at least one bow extending between opposing collars within the stand-off circumferential portion, wherein the at least three centralizers are spaced axially apart and fixedly attached to the tubular with the respective circumferential stand-off portions angularly offset from one another to provide 360 degrees of standoff.
 11. The apparatus of claim 10, wherein fixedly secured comprises rotationally stationary and axially moveable relative to the tubular.
 12. A method comprising: providing a centralizer having opposing collars spaced apart from one another along a longitudinal axis, each of the opposing collars adapted to be fixedly secured to a tubular with a holding force; and a bow extending between the opposing collars, the bow having an at least one apex and a stand-off force.
 13. The method of claim 12, wherein fixedly secured comprises securing the collar to the tubular in a manner to be rotationally stationary relative to the tubular.
 14. A method comprising connecting at least two centralizers to a tubular, each centralizer having a first circumferential stand-off portion and a second circumferential portion together defining 360 degrees, at least two bows extending between opposing collars within the stand-off circumferential portion, wherein the at least two centralizers are spaced axially apart and attached to the tubular with the respective circumferential stand-off portions angularly offset from one another to provide 360 degrees of standoff. 